A known power seat slide apparatus for a vehicle, which is disclosed in for example Japanese Patent No. 2883804, includes a lower rail fixedly mounted on a floor of a vehicle and an upper rail freely slidably supported by the lower rail and supporting a seat of the vehicle. The lower rail has an internal space, which extends in a longitudinal direction of a vehicle, and an opening, which opens or releases an upper portion of the internal space. This power seat slide apparatus further includes a metal-made housing and a resin-made nut member, a screw shaft, and a driving mechanism. The metal-made housing is fitted into the internal space of the lower rail via the opening and is secured to the lower rail. The resin-made nut member is housed inside the housing. The screw shaft extends along the longitudinal direction inside the internal space and is screwed together with the nut member by being freely rotatably supported by the upper rail. The driving mechanism is supported by the upper rail and drives the screw shaft to rotate.
In the above-described power seat slide apparatus, the screw shaft can be rotated relative to the nut member in response to activation of the driving mechanism. Because the screw shaft is screwed together with the nut member, the upper rail can be slidably moved in the longitudinal direction relative to the lower rail secured to the vehicle floor. Therefore, a longitudinal position of the vehicle seat relative to the vehicle floor can be adjusted.
In FIG. 9, the power seat slide apparatus is denoted with a reference numeral 101, the housing is denoted with a reference numeral 143, the screw shaft is denoted with a reference numeral 141, and the nut member is denoted with a reference numeral 142. The housing 143 is press-molded so as to form a sac like structure opening upwardly. A bottom wall 143a of the housing 143 is secured to the lower rail. A reference numeral 149 in FIG. 9 represents a shock-absorbing member.
A load (hereinafter, referred to as a forward impact seat load), which is generated at a time when a vehicle crashes ahead, or a load (hereinafter, referred to as a rearward impact seat load), which is generated at a time when a vehicle is impacted from a rearward, is transmitted, in this order, to the upper rail, the screw shaft 141, the nut member 142, the shock-absorbing member 149, the housing 143 and the lower rail. However, in the power seat slide apparatus 101, because the housing 143 is designed so as to form a sac like structure, a seat load, which is transmitted from the nut member 142 to the housing 143, is subjected to a front wall 143b and a rear wall 143c, of the housing 143, as denoted with an arrow in FIG. 9. Therefore, in order to assure a certain degree of strength of the housing 143, it is necessary to increase a wall thickness of the housing 143 itself. A width dimension W of the housing 143 (a lateral direction of the vehicle) may be enlarged in response to expansion of the wall thickness.
In the above-described circumstances, the internal space of the lower rail has to be enlarged in the lateral direction of the vehicle, which may leads to enlarging the lower rail and the upper rail and to an increase in weight and cost of the power seat slide apparatus.
Moreover, as described above, because the housing 143 is inserted into the internal space of the lower rail via the opening, a lateral dimension of the opening of the lower rail has to be enlarged in response to an increase in the width dimension W of the housing 143. If the kind of power seat slide apparatus is mounted on the vehicle, an appearance of the lower rail may become worse, and foreign substances may easily drop into the internal space of the lower rail.
A need thus exists to provide a power seat slide apparatus for a vehicle, in which a lower rail and an upper rail are downsized, an appearance of the lower rail is enhanced, and foreign substances is restrained from dropping easily into an internal space of the lower rail.